I don't have an example off the top of my head... but just like, Uhm...say two trains are heading toward each other. One is going 40 MPH and the other is going 25MPH. How long would it take for them to meet?

Insufficient info. So, what you ought to do is find a problem you want to work and post your question. Just knowing the speed won't tell you enough to figure out the time. what else do you need? What if one train is pointed east in SF and the other is pointed West in NYC? or what if one is in Missouri? See?

Try an easier problem. Your car is at home. The grocery store is 10 miles away. If your route is a straight line at constant speed of 10 miles per hour, how long will it take you to travel to the store?

try 17 minutes. Use 17/60 ths hours instead of 1/4. See? and just try until the distances of each add to 10, the original distance apart. 10 has to be covered regardless of who goes fast and who goes slow in order for them to meet. That's the problem, more generally.

Okay. I think my problem is I'm a visual learner...so it's more difficult with math. I think in the morning, I'm going to get my friend to help. In my old math class we used to set up a chart, and I was going to do that, but soon realised I didn't remember where the information went.